Imperiled Amazon freshwater ecosystems urgently need basin-wide study, management

The Amazon’s freshwater ecosystems are at risk because current policy and existing protected areas fail to protect the connectivity of the water cycle, scientists warn. The new study, published in Global Change Biology, examines the factors degrading the Amazon basin’s hydrological connectivity: the movement of water — and with it the life-giving matter, nutrients and organisms it carries — between the vast system’s headwaters and the Atlantic Ocean, between the rivers and the forest, and the earth and the atmosphere.

Such connectivity is fundamental to ecosystem health, as it regulates how ecosystems function, the scientists say. The Amazon’s freshwater ecosystems, which cover an area of 1 million square kilometers (386,102 square miles), play crucial roles in regulating climate, transporting nutrients, maintaining water quality, supporting biodiversity, and providing food and fiber, so-called ecosystem services that benefit local, regional and global communities.

If hydrological connectivity is disrupted then the ecosystem can no longer function in the same way and these services may be diminished. This is the danger facing the Amazon.

Lead author Leandro Castello originally studied oceanography, and now works on the conservation of Amazon fish and fisheries, both of which are suffering from habitat change and degradation. “In oceanography they teach you that everything is connected — via water — to everything else. A forested, tropical river basin is not too different: what happens to the trees affects the streams and rivers, and what happens in the headwaters affects everything downstream,” Castello, of Virginia Polytechnic Institute and State University, told Mongabay.

“Everything downstream” can extend for thousands of miles in Amazonia, and include multiple nations and regions with vastly different levels of land and river protection. This political fragmentation makes it difficult to put in place effective basin-wide strategies against ecosystem degradation. “Protected areas [in the Amazon] have limited capacity to protect freshwater ecosystems because they were implemented based on data for terrestrial organisms largely ignoring hydrological connectivity,” Castello explained.

The study examined the impacts of four major drivers of change to the hydrological cycle in the Amazon: dams, mining, land-cover change, and climate change. The scope of the damage being done by these human-caused drivers turned out to be even larger than Castello anticipated. “The surprise was finding how many very strong impacts to the integrity of freshwater ecosystems are happening at such large geographical scale, and yet our policy tools to curb them are less than small,” he warned.

The Amazonian water cycle under attack

Dams have the most obvious and direct effects on hydrological connectivity, but the researchers emphasize that these extend far beyond the reduction of water flow downstream and the flooding of forests backed up behind the dams. Water in reservoirs evaporates at a higher rate than in free-flowing rivers, a river’s thermal regimes can also be affected as reservoir water is released, and seasonal flood dynamics will be attenuated when rising reservoir levels reduce the onrush of annual deluges.

Dams significantly alter floodplain ecology. Amazon floodplains are not only a highly fertile and biologically productive part of the landscape, but flooded forests also provide critical habitat for many species at some point in their life-cycle, including otters, turtles, caimans, and dolphins. As a dam-building boom grips the region, these impacts, which are already significant and widespread, will grow more serious. The authors say that if all planned dams go ahead, only three Amazon tributaries will remain free-flowing in the basin.

Although the mega-dams are the ones making the headlines, thousands of small-scale impoundments also exist in headwater regions to provide irrigation, or drinking water for cattle. Castello’s paper cites one study that found more than 10,000 such dams in the headwaters of a single river, the Xingu. “10,000 small stream dams can potentially have more effect than 1 large hydroelectric dam. It all depends on the context and scale of each driver,” Castello said. “Large and small scale threats need to be addressed. Don’t forget, global climate change was largely caused by that invisible little smoke that comes out of the exhaust of our cars. Strength in numbers can do much harm,” he cautioned.

Land-cover change — most commonly occurring via the cutting of native forest to make way for cattle, crops, or infrastructure — affects the amount of water draining into rivers and being taken up by plants. Again the impacts depend upon scale: locally, deforestation may result in less evapotranspiration (the movement of water from the soil and plants into the atmosphere) therefore increasing run-off into rivers. But over a wider area, the reduction in evapotranspiration can result in less rainfall and drought which reduces the amount of water returning to the forest and to rivers.

Extractive industries, such as mining and oil exploitation, can lead to both deforestation and dam-building, as well as habitat fragmentation, pollution such as oil spills and mercury contamination. With vast areas of the Peruvian, Ecuadorian, Bolivian, and Colombian Amazon designated as concessions for oil and gas exploitation, the impacts in these headwater regions could have far-reaching consequences downstream.

The effects of climate change are also being felt as Andean glaciers melt, and rainfall and drought patterns shift. Extreme weather events and fires, such as those currently raging in parts of the Amazon, are likely to become more common.

The trouble with synergy

What’s more, the numerous impacts identified by the team do not act alone. “Hydrological alterations trigger a wide range of impacts on Amazon freshwater ecosystems, many of which have complex feedbacks and synergistic interactions,” the scientists say. “In the face of these threats, the fate of Amazon freshwater ecosystems depends on a weak and fragmented set of policies that is wholly insufficient to address the growing array of impacts.”

Effective protection of freshwater systems and the water cycle in the Amazon can only come about through a dramatic shift in perspective, Castello explained, and with a research and policy framework that encompasses the Amazon basin in its entirety: “New, basin-wide data can make all the difference, because it would allow scientists, managers, and the public to understand in real-time what is happening and to what extent,” he said. “Policymakers could then make decisions to curb the situation or manage it in the best way possible. This I think would be the spark that we need to develop a basin-wide governance plan that each country can follow.”

“This is not too different from city councils managing neighborhood matters, or county councils managing town issues, and so forth. We do [it] all the time the world over for the issues that we care about,” Castello explained. “So really there is no reason why we cannot do it for the whole Amazon — except of course that nowhere on the planet have we yet managed a river basin as large as this one! All the more reason for us to get started right way.”

The scientists propose satellite monitoring as a holistic method that could be adopted for gathering data across the region. “We suggest that satellite-based measurements provide the most practical approach to monitoring Amazon freshwater ecosystems, as they are the only data source that permits basin-wide inferences about hydrological connectivity and freshwater ecosystem integrity over time,” they write in the study. “Although satellite records cannot directly measure water quality or composition of biotic communities, they can provide useful proxies for ecosystem integrity when combined with other data sources.”

Satellites would be able to monitor the “volume, variability, and timing of water flows,” the researchers assert, making it possible to see how and where these were changing over time.

If basin-wide research and action is not taken, “the consequences are so overwhelming that they are hard to explain,” Castello said. In their paper, the authors outline the broad implications, saying that individual impacts have “the potential to trigger cascading effects that can significantly degrade these freshwater ecosystems. If current trends continue, more tributary basins will be degraded, compromising ecosystem services such as biodiversity maintenance, water quality, flow regulation, C [carbon] cycling, and food production.”

Castello hopes that highlighting these serious issues will raise awareness with the public and with decision makers to help ensure that action is taken. “Public awareness is key. In the 80s, satellite data informed the world of deforestation trends, and allowed the public to complain about it, and management agencies to do something about it (e.g., locating and punishing illegal deforesters),” he said. “We need more data on freshwater ecosystems to [raise public awareness so people] push for similar management actions. The public plays a very powerful role here, though it is hard to separate the public from the scientific and policy arenas, as they often (though not always) go hand in hand.”

“Our paper was intended to get out the message — that these ecosystems are under great threat — in [the] hope it will get a debate going on the topic.”

 

Citation:

Castello, L. and Macedo, M. N. (2015) Large-scale degradation of Amazonian freshwater ecosystems. Global Change Biology, doi: 10.1111/gcb.13173